An object of the present invention is to provide a blood analysis method in which a high level of repeatability and reproducibility is achieved with respect to measurement values in a blood sample, and a blood test kit which is used for the blood analysis method. According to the present invention, a blood analysis method including a step of diluting a collected blood sample with a diluent solution; a step of quantitatively determining sodium ions in the diluent solution of the blood sample by using a solution containing β-galactosidase and at least one substrate which is convertible by β-galactosidase so as to determine a dilution factor from a normal value of serum and blood plasm sodium ions which are homeostatically present in the blood and the quantitative value of sodium ions; and a step of analyzing a concentration of a target component to be measured in the blood sample from the determined dilution factor and a measurement value of a concentration of the target component to be measured in the blood sample, in which the diluent solution is a diluent solution which does not contain sodium ions, is provided.